This application is a continuation of the application Ser. No. 722,864 filed Apr. 11, 1985, now abandoned.
1. Field of the Invention
This invention relates in general to a well drilling apparatus and in particular to a top head drive well drilling apparatus.
2. Description of the Prior Art
Most oil well drilling rigs have a rotary table and a kelly bushing, which rotate a square or hexagonal kelly, attached to a drill string. A top head drive drilling system, however, eliminates the rotary table, the kelly bushing, and the kelly. An electric drilling motor is suspended from a conventional hook, and may also be attached to a carriage, which is guided by a pair of vertical tracks. The drilling motor is connected to the drill string by a cylindrical quill or stem, which extends downward from the motor. A wrench assembly may also be suspended from the drilling motor, in order to break out or make up connections between the stem and the drill string. Such a system is described in patent application Ser. No. 06/600,939, filed Apr. 16, 1984.
When stabbing the top drive quill into the upper end of the drill string, it is necessary to provide a means for aligning the lowest connection on the quill with the upper connection of the drill string. In the past, this function has been provided by a stabbing guide mounted on a transfer elevator. The stabbing guide, when mounted on the transfer elevator, is somewhat cumbersome and requires that the operations for adding a stand of pipe to the drill string be substantially different from the conventional rig operations.